Painters, carpenters, and others using sandpaper sheets often have a difficult time maintaining a supply of such sheets in usable condition. This is especially true when the sheets are exposed to moisture or other hostile environments. A sandpaper sheet can become quite unusable when damp.
Curling of sandpaper sheets can also be a problem, even when the sheets are maintained relatively moisture free. Curled sandpaper sheets are, at the very least, extremely inconvenient to use and it is not at all unusual for curled sheets to be thrown away and not used.